Thermoanalytical and other physical methods will be used in an integrated approach to several problems dealing with the physical and biological properties of lipids and biomembranes. Emphasis will be placed upon combining studies of biological function with physical approaches such as calorimetry and dilatometry. The mechanism for control of fatty acid composition of membranes, especially with respect to its response to temperature, will be studied. A new principle of control based upon the thermodynamic state of the membrane bilayer itself, will be elucidated. The physical rationale for the lipid class composition of membranes will be developed, with initial emphasis upon gram-positive bacteria. A search will be made for the existence of glass transition in lipids and membranes will be made, in order to use such transitions to better understand membrane structure and function. Cholesterol-dipalmitoyl lecithin association will be investigated by using dilatometry, calorimetry, and density-gradient centrifugation to construct a thermodynamic surface in partial specific volume is plotted as a function of temperature and cholesterol concentration. Other relevant model systems will be studied in the same way.